diff --git a/weed/shell/command_collection_delete.go b/weed/shell/command_collection_delete.go
index 545e7830b2..f80c3d9a52 100644
--- a/weed/shell/command_collection_delete.go
+++ b/weed/shell/command_collection_delete.go
@@ -35,7 +35,7 @@ func (c *commandCollectionDelete) HasTag(CommandTag) bool {
 func (c *commandCollectionDelete) Do(args []string, commandEnv *CommandEnv, writer io.Writer) (err error) {
 
 	colDeleteCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
-	collectionName := colDeleteCommand.String("collection", "", "collection to delete. Use '_default' for the empty-named collection.")
+	collectionName := colDeleteCommand.String("collection", "", "collection to delete. Use '"+CollectionDefault+"' for the empty-named collection.")
 	applyBalancing := colDeleteCommand.Bool("apply", false, "apply the collection")
 	// TODO: remove this alias
 	applyBalancingAlias := colDeleteCommand.Bool("force", false, "apply the collection (alias for -apply)")
@@ -55,9 +55,10 @@ func (c *commandCollectionDelete) Do(args []string, commandEnv *CommandEnv, writ
 		return fmt.Errorf("empty collection name is not allowed")
 	}
 
-	// "_default_" stays accepted for compatibility; "_default" is the shared
-	// keyword every other -collection flag uses for the empty-named collection.
-	if *collectionName == "_default_" {
+	// The legacy "_default_" spelling stays accepted for compatibility;
+	// CollectionDefault is the shared keyword every other -collection flag
+	// uses for the empty-named collection.
+	if *collectionName == CollectionDefault+"_" {
 		*collectionName = ""
 	}
 	*collectionName = resolveCollectionName(*collectionName)
diff --git a/weed/shell/command_ec_balance.go b/weed/shell/command_ec_balance.go
index f50bcfe5c3..7dcd4b0d24 100644
--- a/weed/shell/command_ec_balance.go
+++ b/weed/shell/command_ec_balance.go
@@ -44,7 +44,7 @@ func (c *commandEcBalance) HasTag(CommandTag) bool {
 
 func (c *commandEcBalance) Do(args []string, commandEnv *CommandEnv, writer io.Writer) (err error) {
 	balanceCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
-	collection := balanceCommand.String("collection", "EACH_COLLECTION", "comma-separated collection names, wildcards, or regex patterns, \"_default\" for the collection with no name, or \"EACH_COLLECTION\" for each collection")
+	collection := balanceCommand.String("collection", string(wildcard.CollectionFilterEach), "comma-separated collection names, wildcards, or regex patterns, \""+CollectionDefault+"\" for the collection with no name, or \""+string(wildcard.CollectionFilterEach)+"\" for each collection")
 	dc := balanceCommand.String("dataCenter", "", "only apply the balancing for this dataCenter")
 	shardReplicaPlacement := balanceCommand.String("shardReplicaPlacement", "", "replica placement for EC shards, or master default if empty")
 	diskTypeStr := balanceCommand.String("diskType", "", "the disk type for EC shards (hdd, ssd, or empty for default hdd)")
diff --git a/weed/shell/command_ec_common_test.go b/weed/shell/command_ec_common_test.go
index a447800817..22a0c1a1a7 100644
--- a/weed/shell/command_ec_common_test.go
+++ b/weed/shell/command_ec_common_test.go
@@ -14,7 +14,7 @@ func TestCompileCollectionPattern(t *testing.T) {
 		{pattern: CollectionDefault, matches: []string{""}, misses: []string{"pictures"}},
 		{pattern: "pictures", matches: []string{"pictures"}, misses: []string{"", "pictures-backup"}},
 		{pattern: "pictures,videos", matches: []string{"pictures", "videos"}, misses: []string{"", "clips"}},
-		{pattern: "pictures,_default", matches: []string{"pictures", ""}, misses: []string{"clips"}},
+		{pattern: "pictures," + CollectionDefault, matches: []string{"pictures", ""}, misses: []string{"clips"}},
 		{pattern: "pictures*", matches: []string{"pictures", "pictures-backup"}, misses: []string{"clips"}},
 		{pattern: "^pictures", matches: []string{"pictures", "pictures-backup"}, misses: []string{"clips"}},
 		{pattern: "*", matches: []string{"", "pictures"}},
diff --git a/weed/shell/command_ec_encode.go b/weed/shell/command_ec_encode.go
index 7ae07cfcf3..0effe470ab 100644
--- a/weed/shell/command_ec_encode.go
+++ b/weed/shell/command_ec_encode.go
@@ -62,7 +62,7 @@ func (c *commandEcEncode) Help() string {
 	  - Several collections: ec.encode -collection="mybucket,otherbucket"
 	  - Match by prefix: ec.encode -collection="bucket*"
 	  - Match all collections: ec.encode -collection="*"
-	  - The empty-named collection: ec.encode -collection="_default"
+	  - The empty-named collection: ec.encode -collection="` + CollectionDefault + `"
 
 	Options:
 	  -verbose: show detailed reasons why volumes are not selected for encoding
diff --git a/weed/shell/command_ec_rebuild.go b/weed/shell/command_ec_rebuild.go
index 24dfc7af69..9aec3c6ccd 100644
--- a/weed/shell/command_ec_rebuild.go
+++ b/weed/shell/command_ec_rebuild.go
@@ -74,7 +74,7 @@ func (c *commandEcRebuild) HasTag(CommandTag) bool {
 func (c *commandEcRebuild) Do(args []string, commandEnv *CommandEnv, writer io.Writer) (err error) {
 
 	fixCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
-	collection := fixCommand.String("collection", "EACH_COLLECTION", "comma-separated collection names, wildcards, or regex patterns, \"_default\" for the collection with no name, or \"EACH_COLLECTION\" for each collection")
+	collection := fixCommand.String("collection", string(wildcard.CollectionFilterEach), "comma-separated collection names, wildcards, or regex patterns, \""+CollectionDefault+"\" for the collection with no name, or \""+string(wildcard.CollectionFilterEach)+"\" for each collection")
 	volumeIdsStr := fixCommand.String("volumeIds", "", "optional comma-separated list of volume ID to process; defaults to all volumes in the collection")
 	maxParallelization := fixCommand.Int("maxParallelization", DefaultMaxParallelization, "run up to X tasks in parallel, whenever possible")
 	applyChanges := fixCommand.Bool("apply", false, "apply the changes")
diff --git a/weed/shell/command_fs_configure.go b/weed/shell/command_fs_configure.go
index 56bbd5f375..a186ae428c 100644
--- a/weed/shell/command_fs_configure.go
+++ b/weed/shell/command_fs_configure.go
@@ -63,7 +63,7 @@ func (c *commandFsConfigure) Do(args []string, commandEnv *CommandEnv, writer io
 
 	fsConfigureCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
 	locationPrefix := fsConfigureCommand.String("locationPrefix", "", "path prefix, required to update the path-specific configuration")
-	collection := fsConfigureCommand.String("collection", "", "assign writes to this collection; \"_default\" for the collection with no name")
+	collection := fsConfigureCommand.String("collection", "", "assign writes to this collection; \""+CollectionDefault+"\" for the collection with no name")
 	replication := fsConfigureCommand.String("replication", "", "assign writes with this replication")
 	ttl := fsConfigureCommand.String("ttl", "", "assign writes with this ttl (e.g., 1m, 1h, 1d, 1w, 1y)")
 	diskType := fsConfigureCommand.String("disk", "", "[hdd|ssd|<tag>] hard drive or solid state drive or any tag")
diff --git a/weed/shell/command_fs_merge_volumes.go b/weed/shell/command_fs_merge_volumes.go
index f12ada3add..99b6140943 100644
--- a/weed/shell/command_fs_merge_volumes.go
+++ b/weed/shell/command_fs_merge_volumes.go
@@ -67,7 +67,7 @@ func (c *commandFsMergeVolumes) Do(args []string, commandEnv *CommandEnv, writer
 	dirArg := fsMergeVolumesCommand.String("dir", "/", "base directory to find and update files")
 	fromVolumeArg := fsMergeVolumesCommand.Uint("fromVolumeId", 0, "move chunks with this volume id")
 	toVolumeArg := fsMergeVolumesCommand.String("toVolumeId", "", "change chunks to this volume id, or distribute across a comma-separated list of volume ids")
-	collectionArg := fsMergeVolumesCommand.String("collection", "*", "comma-separated collection names, wildcards, or regex patterns; \"_default\" for the collection with no name")
+	collectionArg := fsMergeVolumesCommand.String("collection", "*", "comma-separated collection names, wildcards, or regex patterns; \""+CollectionDefault+"\" for the collection with no name")
 	apply := fsMergeVolumesCommand.Bool("apply", false, "applying the metadata changes")
 	if err = fsMergeVolumesCommand.Parse(args); err != nil {
 		return err
diff --git a/weed/shell/command_fs_merge_volumes_test.go b/weed/shell/command_fs_merge_volumes_test.go
index f7ed2725a8..d02dd60b71 100644
--- a/weed/shell/command_fs_merge_volumes_test.go
+++ b/weed/shell/command_fs_merge_volumes_test.go
@@ -246,9 +246,9 @@ func TestCreateMergePlan_CollectionFilter(t *testing.T) {
 	}
 
 	// "_default" merges only the unnamed-collection volumes.
-	plan, err := newCmd().createMergePlan("_default", nil, 0)
+	plan, err := newCmd().createMergePlan(CollectionDefault, nil, 0)
 	if err != nil {
-		t.Fatalf("_default: %v", err)
+		t.Fatalf("%s: %v", CollectionDefault, err)
 	}
 	if got := plan.targets[needle.VolumeId(1)]; len(got) != 1 || got[0] != needle.VolumeId(2) {
 		t.Fatalf("expected 1->2, got %v", plan.targets)
diff --git a/weed/shell/command_mq_topic_compact.go b/weed/shell/command_mq_topic_compact.go
index 3ade80c154..87c324a036 100644
--- a/weed/shell/command_mq_topic_compact.go
+++ b/weed/shell/command_mq_topic_compact.go
@@ -46,7 +46,7 @@ func (c *commandMqTopicCompact) Do(args []string, commandEnv *CommandEnv, writer
 	topicName := mqCommand.String("topic", "", "topic name")
 	timeAgo := mqCommand.Duration("timeAgo", 2*time.Minute, "start time before now. \"300ms\", \"1.5h\" or \"2h45m\". Valid time units are \"ns\", \"us\" (or \"µs\"), \"ms\", \"s\", \"m\", \"h\"")
 	replication := mqCommand.String("replication", "", "replication type")
-	collection := mqCommand.String("collection", "", "optional collection name; \"_default\" for the collection with no name")
+	collection := mqCommand.String("collection", "", "optional collection name; \""+CollectionDefault+"\" for the collection with no name")
 	dataCenter := mqCommand.String("dataCenter", "", "optional data center name")
 	diskType := mqCommand.String("disk", "", "[hdd|ssd|<tag>] hard drive or solid state drive or any tag")
 	maxMB := mqCommand.Int("maxMB", 4, "split files larger than the limit")
diff --git a/weed/shell/command_volume_fsck.go b/weed/shell/command_volume_fsck.go
index 6bc74dd47e..f62a491e1f 100644
--- a/weed/shell/command_volume_fsck.go
+++ b/weed/shell/command_volume_fsck.go
@@ -111,7 +111,7 @@ func (c *commandVolumeFsck) Do(args []string, commandEnv *CommandEnv, writer io.
 	c.verbose = fsckCommand.Bool("v", false, "verbose mode")
 	c.skipEcVolumes = fsckCommand.Bool("skipEcVolumes", false, "skip erasure coded volumes")
 	c.findMissingChunksInFiler = fsckCommand.Bool("findMissingChunksInFiler", false, "see \"help volume.fsck\"")
-	c.collection = fsckCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; empty or \"*\" matches all, \"_default\" the collection with no name")
+	c.collection = fsckCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; empty or \"*\" matches all, \""+CollectionDefault+"\" the collection with no name")
 	volumeIds := fsckCommand.String("volumeId", "", "comma separated the volume id")
 	applyPurging := fsckCommand.Bool("reallyDeleteFromVolume", false, "<expert only!> after detection, delete missing data from volumes / delete missing file entries from filer. Currently this only works with default filerGroup.")
 	c.forcePurging = fsckCommand.Bool("forcePurging", false, "delete missing data from volumes in one replica used together with applyPurging")
diff --git a/weed/shell/command_volume_grow.go b/weed/shell/command_volume_grow.go
index 20b4f2f27e..b1f11d8694 100644
--- a/weed/shell/command_volume_grow.go
+++ b/weed/shell/command_volume_grow.go
@@ -39,7 +39,7 @@ func (c *commandGrow) Do(args []string, commandEnv *CommandEnv, writer io.Writer
 
 	volumeVacuumCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
 	growCount := volumeVacuumCommand.Uint("count", 2, "")
-	collection := volumeVacuumCommand.String("collection", "", "grow this collection; \"_default\" for the collection with no name")
+	collection := volumeVacuumCommand.String("collection", "", "grow this collection; \""+CollectionDefault+"\" for the collection with no name")
 	dataCenter := volumeVacuumCommand.String("dataCenter", "", "grow volumes only from the specified data center")
 	rack := volumeVacuumCommand.String("rack", "", "grow volumes only from the specified rack")
 	dataNode := volumeVacuumCommand.String("dataNode", "", "grow volumes only from the specified data node")
diff --git a/weed/shell/command_volume_mark.go b/weed/shell/command_volume_mark.go
index 5d0f2f0ee7..443a7a943a 100644
--- a/weed/shell/command_volume_mark.go
+++ b/weed/shell/command_volume_mark.go
@@ -48,7 +48,7 @@ func (c *commandVolumeMark) Do(args []string, commandEnv *CommandEnv, writer io.
 	volMarkCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
 	volumeIdInt := volMarkCommand.Int("volumeId", 0, "the volume id")
 	nodeStr := volMarkCommand.String("node", "", "the volume server <host>:<port>")
-	collection := volMarkCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; \"_default\" for the collection with no name")
+	collection := volMarkCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; \""+CollectionDefault+"\" for the collection with no name")
 	writable := volMarkCommand.Bool("writable", false, "volume mark writable")
 	readonly := volMarkCommand.Bool("readonly", false, "volume mark readonly")
 	readonlyCanDelete := volMarkCommand.Bool("readonlyCanDelete", false, "volume mark readonly but still accepting deletes")
diff --git a/weed/shell/command_volume_tier_move.go b/weed/shell/command_volume_tier_move.go
index 0d0ac97be2..11a8481a9a 100644
--- a/weed/shell/command_volume_tier_move.go
+++ b/weed/shell/command_volume_tier_move.go
@@ -67,7 +67,7 @@ func (c *commandVolumeTierMove) Help() string {
 
 	Note:
 		-collectionPattern is a comma-separated list of collection names, with "*" and "?"
-		wildcards, and regex patterns. Use "_default" to match only the default collection
+		wildcards, and regex patterns. Use "` + CollectionDefault + `" to match only the default collection
 		(volumes with no collection name). An empty pattern matches all collections.
 
 `
diff --git a/weed/shell/command_volume_vacuum.go b/weed/shell/command_volume_vacuum.go
index e162b161cd..f047116d91 100644
--- a/weed/shell/command_volume_vacuum.go
+++ b/weed/shell/command_volume_vacuum.go
@@ -44,7 +44,7 @@ func (c *commandVacuum) Do(args []string, commandEnv *CommandEnv, writer io.Writ
 
 	volumeVacuumCommand := flag.NewFlagSet(c.Name(), flag.ContinueOnError)
 	garbageThreshold := volumeVacuumCommand.Float64("garbageThreshold", 0.3, "vacuum when garbage is more than this limit")
-	collection := volumeVacuumCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; empty or \"*\" matches all, \"_default\" the collection with no name")
+	collection := volumeVacuumCommand.String("collection", "", "comma-separated collection names, wildcards, or regex patterns; empty or \"*\" matches all, \""+CollectionDefault+"\" the collection with no name")
 	volumeIds := volumeVacuumCommand.String("volumeId", "", "comma-separated list of volume IDs")
 	if err = volumeVacuumCommand.Parse(args); err != nil {
 		return nil
diff --git a/weed/shell/command_volume_vacuum_test.go b/weed/shell/command_volume_vacuum_test.go
index 608623169e..a8ec288646 100644
--- a/weed/shell/command_volume_vacuum_test.go
+++ b/weed/shell/command_volume_vacuum_test.go
@@ -108,12 +108,12 @@ func TestVacuumRequestsForPattern(t *testing.T) {
 
 	// The unnamed collection resolves to per-volume requests — no Collection
 	// value selects it alone, and read-only volumes stay skipped.
-	reqs, err = vacuumRequestsForPattern(topo, mustMatcher(t, "_default"))
+	reqs, err = vacuumRequestsForPattern(topo, mustMatcher(t, CollectionDefault))
 	if err != nil {
-		t.Fatalf("_default: %v", err)
+		t.Fatalf("%s: %v", CollectionDefault, err)
 	}
 	if len(reqs) != 1 || reqs[0].VolumeId != 2 || reqs[0].Collection != "" {
-		t.Fatalf("_default: got %v, want one per-volume request for volume 2", reqs)
+		t.Fatalf("%s: got %v, want one per-volume request for volume 2", CollectionDefault, reqs)
 	}
 
 	// A filter hitting nothing is an error, not a silent no-op.
@@ -140,7 +140,7 @@ func TestVacuumRequestsForVolumeIds(t *testing.T) {
 	}
 
 	// The unnamed collection sends a volume-id-only request.
-	reqs, err = vacuumRequestsForVolumeIds(topo, mustMatcher(t, "_default"), []uint32{2})
+	reqs, err = vacuumRequestsForVolumeIds(topo, mustMatcher(t, CollectionDefault), []uint32{2})
 	if err != nil {
 		t.Fatalf("vid 2 in default: %v", err)
 	}